It is well known that good control of type 1 diabetes mellitus (T1D) decreases long-term complications, such as eye disease (retinopathy), kidney damage (nephropathy), and nerve damage (neuropathy). Children and adolescents with poorly controlled T1D are at high risk to develop these diabetes-related complications in adulthood, and thus they stand to gain the most from improving their control. There are many possible reasons for poorly controlled diabetes, including poor compliance with home blood glucose monitoring. Not having blood sugar data prevents proper insulin dosing, especially when blood sugars are elevated requiring extra rapid- acting insulin. Continuous glucose monitoring (CGM) allows the measurement of blood sugars in real time without repeated fingerstick blood sugar checks. However, patients using CGM devices are still supposed to use fingerstick blood sugars for making treatment decisions, such as treating low or high blood sugars. Recognizing how [infrequently patients with poorly- controlled T1D] check their BGs, it is important to explore whether blood sugar data generated via CGM and used for treatment decisions would be better than their usual lack of glucose data. We therefore propose a study that will evaluate CGM use in real time in pre-adolescents and adolescents with poorly controlled T1D without the mandatory confirmation of the blood sugars by fingerstick. We hypothesize that diabetes control will improve because these patients will use sensor data to make treatment decisions rather than fingerstick blood sugars that are done too infrequently. [Twenty-six] patients between 10 and 18 years old with poorly controlled T1D will be enrolled in this 9-month pilot study. After having a CGM device for one week, patients who actually used the CGM who want to continue the study will be randomized to either CGM or Standard Care. After three months, CGM use will be initiated in subjects in the Standard Care group; patients in the CGM group still using CGM will continue to do so. Enrolled patients will be followed for an additional 6 months. Study outcomes will include changes in diabetes control (based on A1c), several glycemic indices, frequency of CGM use, and frequency of BG checks. The results from this pilot study will be used to create a larger trial with more subjects with poorly-controlled T1D.